The often-ignored technical reasons behind the problematic behaviour of certain wall-mounted heat pumps in Montréal and Québec’s colder regions
Every winter, our teams receive calls from concerned customers reporting that their wall-mounted heat pump constantly switches to defrost mode, sometimes every 30 minutes—even without visible frost buildup. This frequent defrosting, common in Montréal, Laval, Longueuil, the North Shore and the South Shore, reduces thermal comfort, increases power consumption, and shortens the system’s lifespan.
At AirGreen, we’ve been installing and servicing HVAC systems (heating, ventilation, and air conditioning) for years, even in the harshest winter conditions Québec can throw at us. In this article, we clearly explain why certain wall-mounted heat pumps enter defrost mode too often, which brands are most affected, how to prevent this issue, and the professional solutions we recommend.
Understanding the defrost cycle of wall-mounted heat pumps
Before jumping to conclusions about malfunction, it’s important to understand how defrosting works:
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When a wall-mounted heat pump is in heating mode, it draws heat from the outside air and transfers it indoors.
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In cold and humid climates, this process creates condensation, which freezes on the outdoor coil.
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To prevent this frost buildup from blocking heat exchange, the heat pump periodically switches to defrost mode: it reverses its cycle, blows cold air indoors temporarily, and heats the coil to melt the frost.
This cycle is normal. But when the unit switches to defrost mode too often, it usually signals an underlying issue.
The main reasons behind excessive defrosting in winter
Here are the most common causes we’ve encountered during service calls and installations across Greater Montréal:
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Poor placement of the outdoor unit
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A unit that’s poorly oriented (facing wind or permanently shaded) accumulates more frost.
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A unit installed too close to the ground prevents proper drainage of defrost water.
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Brands or models not suited for Québec’s climate
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Some heat pumps designed for milder climates don’t perform well in Québec winters.
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Models without intelligent defrost control activate defrost mode based solely on low temperature readings—without verifying if there’s actual frost.
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Faulty or poorly calibrated frost sensor
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If the sensor detects frost when none is present, the system goes into defrost unnecessarily.
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This is a recurring issue with certain low-end brands.
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Neglected HVAC maintenance
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A dirty coil or fan blocked by leaves impedes heat exchange.
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Buildup of debris accelerates frost formation, leading to more frequent defrost cycles.
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Real-world case studies from the Montréal area
We’ve encountered several such cases during recent service visits:
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In Laval, a client who bought a generic brand heat pump online experienced defrost cycles every 25 minutes at just -5°C. The unit was installed without elevation, fully shaded, and poorly oriented. The result: poor performance and constant discomfort.
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In Longueuil, a unit installed by a non-certified technician stopped heating at the first cold snap. After diagnosis, we found a miscalibrated frost sensor and an electronic board incompatible with local climate conditions.
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In Sainte-Thérèse, we replaced a low-end wall-mounted heat pump with a Gree Extreme 18,000 BTU model built for cold climates. The outcome: less frequent defrosting, improved comfort, and a 32% drop in the electricity bill.
The brands most prone to excessive defrost cycles
Based on our field experience, we’ve identified some brands that consistently underperform in our climate:
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Asian models not designed for -20°C or lower
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Products lacking ENERGY STAR certification
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Units sold online with no local service or calibration options
At AirGreen, we refuse to install certain brands precisely for these reasons.
How AirGreen avoids this issue during installation
Our professional HVAC installations include:
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Thorough analysis of the optimal outdoor unit placement, factoring in wind exposure, sunlight, and drainage access
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Use of locally tested brands like Fujitsu, Gree, Sharp ZU1, Bosch BIVA, Lennox, all equipped with intelligent defrost management
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Elevation using winter-ready bases, ensuring proper water drainage
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Correct positioning and calibration of sensors
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Preventive maintenance (cleaning the outdoor unit, checking coils, verifying sensors)
Practical tips for homeowners during winter
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Keep an eye on your outdoor unit: if thick frost persists even after several defrost cycles, call a professional.
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Have your wall-mounted heat pump serviced every fall, before the deep cold sets in.
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Make sure the unit isn’t obstructed by snow, ice, or debris.
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Choose a heat pump certified for cold climates.
Conclusion: A proper HVAC installation avoids a lot of trouble
Excessive defrosting isn’t inevitable. It’s often a sign that the heat pump is poorly chosen or poorly installed. At AirGreen, we believe every client deserves optimal comfort—even at -30°C.
Our experts serve all of Montréal, Laval, Longueuil, the North Shore and the South Shore, delivering HVAC solutions that are reliable, efficient, and tailored to Québec’s climate.
Need a diagnosis or a replacement? Contact AirGreen for trusted expertise and certified solutions.